Behaviors of oil-soluble molybdenum complexes to form very fine MoS₂ particles in vacuum residue

Dispersion and thermal behaviors of oil-soluble Mo-dithiocarbamate (Mo-DTC) and Mo-dithiophosphate (Mo-DTP) as the MoS₂ catalyst precursors were studied in petroleum vacuum residue (VR) using FT-Far IR, XRD and TEM. FT-Far IR was proved to detect the Mo complexes and their derived MoS₂ in VR without the interference of the complicated organic matrix. Their transformation into MoS₂ was identified by detecting the changes in the ligand bonds and crystal structure. These complexes were found to be distributed in asphaltene (or maltene) by fractionation with hexane due to their solubility in the heavy oil, ruling out any chemical interaction of the complex with asphaltene. Mo-DTC was found to be decomposed at 350°C to form definite MoS₂ in VR. Mo-DTP started its decomposition around 200°C, and however, no definite formation of MoS₂ was confirmed by heating up to 500°C. Dispersion of the complexes in VR and asphalthene was always good as indicated by TEM. Both complexes in VR at 380°C under hydrogenation (HYD) conditions provided more or less MoS₂. H₂S and reactive sulfur species were assumed to accelerate the transformation of the Mo complex to MoS₂ during HYD reaction. Some difficulty of Mo-DTP to be transformed quantitatively into definite MoS₂ in VR may explain its poor activity for up-grading VR.